Scientists discover deer migration route in Grand Teton

National Park Service employees Jess Erwin, Pete Mumford, and Sarah Dewey process and collar a doe mule deer In Grand Teton National Park. GPS equipped tracking collars are providing new insight into deer migration routes to and from the park.(Grand Teton National Park)

Sarah Dewey didn’t know where the deer she collared with a GPS tracker in November would go.

Most of the deer she’d collared in Grand Teton National Park since 2013 headed to east to the North or South Fork of the Shoshone River. This one? The National Park Service wildlife biologist would just have to wait and see.

Dewey couldn’t have predicted what she saw this spring in the data. The deer headed generally west — around the the North end of Jackson Lake, across the Snake River and up the eastern flank of the Teton Range. Eventually it crossed the mountains and descended their west slope into Idaho. Its 45-mile trek to winter range included more than 2,000 vertical feet of climbing. It was a path Dewey hadn’t yet seen.

This newly discovered migration route is one of four recently documented in an effort to better understand where Grand Teton’s mule deer go when they leave the park.

The park started studying animal migration in the late 1990s with species such as red-tailed hawks and osprey. Eventually they started using radio collars to track moose, bison and bighorn. But migrations, particularly long-distance ones, were difficult to document.

It wasn’t until GPS collars became widely available about 15 years ago that researchers could collect location data on animals wherever they moved, for years at a time. The new technology allowed for projects like delineating the famed “path of the pronghorn” migration in the early 2000s, Dewey said.

Though it often seems that there is little left to discover, big ecological questions persist. Only with recent advances in technology are many of those question now being answered — like where do Grand Teton’s mule deer go for the winter?

“If we want to conserve biodiversity within the park, we need to have all the pieces of the big picture,” Dewey said. “A lot of these animals spend a large portion of the year outside the park.”
Mule deer summer in Grand Teton but scientists didn’t know where they were going in the fall, what obstacles they faced en route, or what conservation efforts could help the population thrive. “We need the detailed information about the routes they use,” Dewey said.

Data from GPS collars have revealed four distinct mule deer migration routes to winter ranges outside of the park (Grand Teton National Park)

Biologists placed GPS collars on two deer in 2013 as a pilot study in Grand Teton. One deer they collared near Flagg Ranch and the other near Colter Bay. Dewey expected the deer to head west, but both animals went east. One traveled about 66 miles in about 10 days to the North Fork of the Shoshone River. The other spent about two weeks crossing nearly 75 miles to the South Fork of the Shoshone. The latter crossed several high mountain passes and the Absaroka Divide on its journey.

“It’s pretty amazing what these animals do in order to make it work,” Dewey said.
Dewey and her colleagues collared six more deer in 2014 in the northern part of Grand Teton.
One went to the North Fork of the Shoshone. Four went to the South Fork area. One went along the Teton Front to the Gros Ventre drainage and across the Continental Divide. It wintered near Dubois 95 miles from where it started.

Biologists had anecdotal and observational information on where the deer were migrating. “What’s new is that we are finally able to detail these migrations,” Dewey said.

Last fall researchers collared four more deer in the park. Three headed east to the South Fork of the Shoshone. But that one, it struck up Webb Canyon deep in the Teton backcountry and traveled those 45 miles west to Idaho, marking a route that was new to scientists and identifying the fourth long-distance migration route to-and-from the park. Scientists had known that deer traveled between the park and Idaho, but they didn’t know what route deer traveled.

Dewey wants to collect more data. It takes more than one animal to make a scientifically valid sample and to really tell scientists what the migration experience is like on each route. She plans to collar more deer and continue building the data. She hopes at least a few will go to Idaho, or to Dubois, but she never knows where the deer will head.

The park is also a partner with the Wyoming Migration Initiative, which this spring launched a large mule deer movement study across the state. While park staff conducted its collaring separately in Grand Teton, both projects are interested in long-term conservation of migration corridors. Dewey is interested to learn if some of the deer collared in the migration initiative study make their way to the park.

Tracking and sharing the migration data is just the start. The next piece will include talking with agencies, non-government organizations and private landowners about conserving migration routes.

“If we want to keep seeing mule deer in Grand Teton in the summer,” Dewey said, “we need to make it a priority to understand their needs, and where they travel, and work to conserve those, too.”

GPS collars, like the one attached to this mule deer doe, can be programed to fall off after a certain amount of time. (Grand Teton National Park)

About Kelsey Dayton

Kelsey Dayton is a freelancer and the editor of Outdoors Unlimited, the magazine of the Outdoor Writers Association of America. She has worked as a reporter for the Gillette News-Record, Jackson Hole News&Guide and the Casper Star-Tribune. Contact Kelsey at [email protected] Follow Kelsey on Twitter at @Kelsey_Dayton